Continuous floating zone refining system



July 1, 1969 J. K. KENNEDY ETAL CONTINUOUS FLOATING ZONE REFINING SYSTEM Sheet L of 3 Filed June 11, 1965 *UII Nu QM nwflil NEE! 3 A M ww K v M Q Mg Sn INVENTOM JOHN K KENNEDY GUY I]. 0,4755 BY 4 nr'r-amlrs' J. K. KENNEDY ETAL 3,453,370

CONTINUOUS FLOATING ZONE REFINING SYSTEM Filed June 11. 1965 July 1, 1969 y 1, 1969 J. K. KENNEDY E AL 3,453,370

' CONTINUOUS FLOATING ZONE REFINING SYSTEM v Filed June 11. 1965 Sheet ,2 of 3 INVENTOR$ JOHN 2r. KEN/V50) and Guy '71- M04715;

United States Patent 3,453,370 CONTINUOUS FLOATING ZONE REFINING SYSTEM John K. Kennedy, Boston, and Guy H. Moates, Lexington, Mass., assignors to the United States of America as represented by the Secretary of the Air Force Filed June 11, 1965, Ser. No. 463,409 Int. Cl. HtlSb 7/18 US. Cl. 13-26 11 Claims ABSTRACT OF THE DISCLOSURE A continuous floating zone refining system conducted under vacuum conditions where a portion of an ingot is heated intermediate its length by a heater, and feed material is deposited at the heated portion followed by Zone refining said ingot by causing a narrow molten zone to progress along the length of the ingot until the position of deposited material is reached, at which time the ends of the ingot are pulled to reduce the section on which material has been deposited to unit cross section and continuing the progression of the molten zone along the remaining length of the bar, after which the system is repeated.

The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to us of any royalty thereon.

This invention relates generally to zone refining, and more particularly, to a continuous floating zone refining system which is utilized for providing ultra-pure inorganic or organic materials.

Presently, the floating zone technique of zone refining is limited to a batch process which has inherent limitations. Floating zone refining, however, has advantages over other modes of zone refining in that many sources of contamination are eliminated. For example, the leaching of impurities from the container is eliminated since the material itself acts as its own container. When induction heating provides the molten zone in the process, only the material to be treated has its temperature raised. In addition, atmospheric contamination may be eliminated by conducting the process under vacuum conditions or with a chosen ambient gas. Unlike many forms of refining, the floating zone refining system may be regulated to provide a single crystal product.

Accordingly, it is a primary object of this invention to provide a purification system which combines the advantages of floating zone refining with those of continuous operations.

It is another object of this invention to provide a continuous floating zone refining system wherein it is possible to approach a steady state that very closely approximates the ultimate distribution of impurities along an ingot such that, upon attainment of steady state conditions, the material produced by the system has constant solute concentration.

It is still another object of this invention to provide continuous floating zone refining wherein the bar of material to be refined acts as its own container.

It is a further object of this invention to provide a floating zone refining system which is continuous and which utilizes surface tension for holding a zone in position.

A still further object of this invention involves the provision of a floating zone refining system with is cgntinuously operated and utilizes addition of feed by thermal decomposition of a vaporizable compound of the material undergoing treatment or by a vapor transport of the bar material.

3,453,370 Patented July 1, 1969 Another object of this invention involves the provision of a continuous floating zone refining system which is capable of producing material of constant composition at near ultimate purity in poly-crystalline or single crystal form.

Still another object of this invention involves a floating zone system in which the bar or ingot undergoing treatment comprises an enriching, feeding and stripping section of a continuous zone refining system.

A further object of this invention involves a continuous floating zone refining system from which product and waste are produced at each pass.

A further object of this invention involves the provision of a continuous floating zone refining system which may be operated under vacuum conditions or with any desired ambient gas.

A still further object of this invention involves the provision of a continuous floating zone refining system which is capable of intermittent operation.

Another object of this invention involves the provision of a continuous floating zone refining apparatus which is easily produced and utilizes conventional, currently available materials that lend themselves to mass production manufacturing techniques.

These and other advantages, features and objects of I the invention will become more apparent from the following description taken in connection with the illustrative embodiments in the accompanying drawings, wherem:

FIGURES 1 through 4 are schematic representations of the apparatus at difierent stages of the floating zone refining process;

FIGURES 5 and 6 are detailed drawings of the grips illustrated schematically in FIGURES 1 through 4 and their means for operation; and

FIGURE 7 is a schematic representation of an alternative embodiment of the apparatus without feed-through seals, which is more easily capable of intermittent operation.

In order to explain the apparatus of this invention the following assumptions are made, although they are not intended to limit the scope of the invention:

(1) The system undergoing treatment is an ideal binary solute-solvent system;

(2) The solute is the impurity to be separated;

(3) The distribution coefficient k is constant and less than 1; and

(4) The density of the solid and liquid phases are equal.

Referring to FIGURES 1 through 4 the apparatus comprises a bar or ingot 10 of the material to be zoned and purified. The ingot 10 is held in position by a pair of hollow grips 12 and 14 which are adjustable in a manner later to be described relative to FIGURES 5 and 6. The grips 12 and 14 can be provided to apply varying degrees of force on the ingot to a point of release. In addition, the grips may also be capable of movement in directions toward and away from each other.

In order to eliminate atmospheric contamination a container or enclosure 16 of any suitable material, such as glass, is provided. In order to maintain vacuum conditions with a vertically movable ingot 10 in container 16, vacuum feed-through seals 18 and 20 of a conventional type, e.g., Wilson feed-through seals, are provided. The container 16 is also provided with ports 22 and 24 to which conventional fittings and valves would be secured in order to allow for connection with a vacuum system and/ or an ambient gaseous atmosphere for insertion into the container.

Assuming that the bar 10 is of unit cross section, that between the grips 12 and 14 the bar is of a length m and of a weight M, and that a portion of the bar between the grips 12 and 14 is of a weight L and of a length l, the system would be operated in the following manner. With a direction of travel of the zones from bottom to top, and with the freezing interface of the molten zone regenerating the bar at unit cross section, a steady state condition is assumed to have been reached after a large number of passes of the zone has traversed the bar in the manner described below.

As shown in FIGURE 1, an induction heater 26 is positioned as shown intermediate the ends of the length l. The output of the heater 26 is adjusted to heat the bar to a predetermined temperature. At this time, enclosure 16, which had been evacuated through one of ports 22 and 24, would have one of the ports switched to a source of gas which could be a compound of the material undergoing treatment and which is volatile at the temperature of the entire system. A carrier gas or other gas which could aid in the decomposition could be included, if desired. Alternatively, the material may be sputtered onto the ingot by any conventional means, for example, by an electron beam arrangement. The temperature of the entire system could be varied by external means, not shown, such as a separate heater coil surrounding the container 16. The temperature of the zone of the bar 10 which is heated by induction heater 26 is such that the compound, when a compound of the material undergoing treat-ment is utilized, decomposes at the heated zone, thereby depositing the bar material in the gas on the bar at the heated zone. The port not used as an inlet would become an exit port and would provide a means for escape of the other component or components of the gas for their sweep out of the enclosure.

If the zone is heated by the heater 26 during the decomposition, a build-up of the bar material will occur in this zone as shown at 28, FIGURE 2. The heater 26 would then shut off or quickly move to the bottom of the length 1 (FIGURE 2 in phantom), create a molten zone, and cause the molten zone to move up the bar as in conventional batch float zone refining. When the molten zone gets to the plane where the deposit 28 begins, the grip or grips 12 and/ or 14, move upward, downward or, preferably, apart to stretch sufficiently the bar at the molten zone so that, at the freezing interface, the molten zone will continue to generate a bar of unit cross section, as illustrated in FIGURE 3. Once the region 28 has been passed by the molten zone, conventional batch float zone refining continues in normal fashion.

When a pass of the molten zone has traversed the bar to the topmost point 0+1), processing a weight of material L-l-F (where F is the weight of material added to the bar via decomposition, shown at 28, FIGURE 2), the heater 26 is shut down, thereby allowing the last zone of the bar to freeze (by normal or uniform freeze, for example). The length of the original 'bar I has now stretched and been processed to the length l+f, FIGURE 3 (where fis the length of the cylinder of unit cross section that the weight of material F can generate). The grips 12 and 14 are now moved toward each other a total distance equal to 1. Then, the length of the bar between the grips 12 and 14 is m, FIGURE 4, or the original length of the bar as shown in FIGURE 1. The process is then repeated when another zone is passed through the bar. The planes 3030 and 3232 clearly illustrate in FIGURES 1 through 4 the stretch of the bar and, accordingly, the removal of product and waste. As can be seen :in FIGURES 1 and 2, the planes are drawn through a point in the bar lying just external to the feedthrough seals 18 and 20. In FIGURES 3 and 4 the same point on the bar has been moved by the stretching action to obtain unit cross section. The distance each plane has moved is related to the amount of material deposited and its stretching to unit cross section. When the process has been repeated, assuming a constant addition of material, the planes would move further apart by a distance of When the heater 26 melts a zone of the bar in order to obtain a decomposition of the gas and to cause a deposition or addition of the feed material, the adjustable grips 12 and 14 can be moved with respect to each other at the time of feed so that, when the decomposition is stopped, the heater shuts off, the zone is allowed to freeze and the bar will still be of unit cross section throughout. Since the hump 28 is eliminated, the bar would appear as shown in FIGURE 3. The length of bar between the grips 12 and 14 would be m+f and the length of travel of the zone would be, as before 1+ After the zone has been put through the bar, the grips 12 and 14 would be adjusted to give a distance between them of length l and, as above, the process would then be repeated when additional passes are required.

In the processes described above the adjusting of the grips 12 and 14 to restore the length of bar between them to a length I (from f-l-l) will determine how much waste and product will be produced by the system per pass. The sum of the weight of product P and the waste W produced per pass must equal F. Thus,

If the feed is added to the bar as a deposit 28, FIG- URE 2, then, during the passage of the molten zone when the zone encounters the deposit, the grips 12 and 14 must move apart to maintain the freezing interface cross section at unity. The amount each grip moves must be carefully noted. The total length moved by both grips is f. After the pass has been completed the grips 12 and 14 must move together so that the distance between them will again be m. The amount of movement each grip makes in maintaining constant cross section must be taken into account to assure that the plane of the bar 10 shown as 30-30 in the FIGURES has moved up a distance w and that the plane 3232 has moved down a distance p. The distances w and p are, respectively, the lengths of bar of unit cross section to which the weights W and P correspond. For the method of decomposition, wherein the heated zone at which decomposition takes place is molten, a similar accounting of grip movement must be made to assure that after each pass the planes 3030 and 3232 have, before the start of the succeeding pass, moved respectively w and p.

A mechanism for operating the grips 12 and 14 is shown in FIGURE 5 wherein the grip portion is in the form of a split cylinder 40 having spring means 42 between the adjacent halves in order to exert a force tending to separate them. The bar or ingot 10 lies within the bore of the split cylinder 40 and is clamped by means of a notched, belt-like portion 44 of the clamp means 46. A motor 48 is arranged to drive a worm within the casing 50, which engages the belt portion 44. The operation of the clamp 46 is based on the principle of conventional automotive radiator or heater hose clamps except that the worm gear is motor driven.

In order to produce the necessary longitudinal motion of the grips along the axis of the ingot a motor driven worm gear arrangement 52 is provided to mesh with a longitudinally movable worm rack 54 to which the holder 12 and/or 14 is secured. The rack is shaped like a rail and is arranged to slide within a guide post 56 which would be secured to the outer container 16, as is the motor unit 52.

Thus, operation of motor 48 would produce a tightening and release of the holder about the ingot 10-, while unit 52 would produce longitudinal motion of the holder along the ingot and/ or a stretching of the ingot, depending upon whether clamp 46 is in engagement with the ingot 10. Both or only one of the holders may be provided with unit 52; however, it is preferred that both be operable longitudinally. 'In either case the release means is required for all of the holders.

An alternative embodiment of the gripping means is shown in FIGURE 6 which utilizes a hollow cylindrical housing 60 which is fixedly secured to the container 16.

The ingot is engaged by means of rollers 62 journalled in housing 60. A motor worm unit 64 is arranged to drive one or more of the rollers 62, which would be serrated, by engagement of the worm unit 64 with worm gear 66. As shown, the gear 66 may be formed as an integral part of the roller. Operation of the motors in the same direction for both holders 12 and 14 would cause a movement of the ingot 10 axially; however, opposite movement of the serrated rollers 62 of each holder by means of its motor unit 64 would produce a stretching of the ingot in order to provide the required reduction in diameter as previously specified.

Thus, there has been described an apparatus and process for providing enriching, feeding and stripping actions which are all contained in the bar or ingot 10. At the start of the decomposition step, before material to be decomposed is admitted to the enclosure 16, the heater 26 has heated a zone of the ingot intermediate between the extremities of the length l; the portion of the length l of ingot 10 below the heated zone is the enriching section, and the portion of the length l of ingot 10' above the heated zone becomes the stripping section (assuming k l). The material in the heated zone plus the material added by the decomposition F, comprises the feed section. The product and waste exit from enclosure 16 would be via the feed-through seals 20 and 18. Once outside of the enclosure the product and waste may be separated from the bar 10' by any conventional means, not shown, for example, an appropriate saw.

The apparatus thus far described requires that the ingot 10 be maintained at constant cross section; however, when irregularities occur, the feed-through seals wear excessively and may leak. Accordingly, separate die elements 19 and 21 (FIGURE 4) may be placed within the container 16 adjacent the seals 18 and 20 in order to assure a smooth, regular surface being presented to the seals.

Since the process of this invention, unlike the usual continuous refiners, lends itself easily to interruptions in the production without adversely affecting the product, an intermittent, continuous process is described relative to the embodiment of FIGURE 7. This process and the apparatus therefor has the advantage of eliminating feedthrough seals and allows the processing of predetermined amounts of material from various ingots on order with the same equipment.

Referring to FIGURE 7, wherein like elements are numbered the same as corresponding elements in the previous embodiments, 10 represents the ingot to be processed within a container 70 which has elongated end caps 72. The main body portion of 70 must be detachably secured to the end caps. For vacuum conditions, for example, the main body portion could have a rolled edge 74 at each end which mates with a correspondingly curved flange 76 with a seal means provided between the two mating portions 74, 76; however, any conventional joining means may be utilized. As in the previous embodiment, ports 22 and 24 are provided for the same functions.

The ends of the ingot 10 have provided thereon chucks 78 which comprise a mass of magnetizable material 79 on the outer periphery of the ingot engaging portion. In order to position the ing-0t, a pair of magnets 80' surround the container 70 adjacent the chucks 78 with provision for the lengthening and movement of the ingot 10 by the magnets 80 being performed by a worm and gear arrangement 82 generally attached to the magnets. To aid in guidance of the ingot and to maintain its location centrally within the container 70, guide rollers 92 are provided. It is contemplated that the rollers would be mounted on leaf springs 84 which in turn would be secured to a flexible band 86 which is engaged in a notch 88 within the walls of the body section of the container 70.

Since balance of the system requires accurate control of the lengthening of the ingot, verniers may be provided 6 as illustrated at on FIGURE 7. Similarly, verniers may be provided with the worm and gear arrangements of the embodiments of FIGURES 5 and 6.

Operation of the embodiment of FIGURE 7 would proceed as described relative to FIGURES 1 through 4; however, when a desired length of material has been processed or when the ingot extends to the ends of end portions 72, the process is shut down, the end portions 72 removed and the required amounts of material are then sawed from the ingot. After this operation a new ingot or the same ingot would be processed until shut down time is indicated.

This invention, therefore, provides operative systems for performing floating zone refining in a continuous manner, thereby combining the advantages of floating zone refining and completely continuous operation.

Although the invention has been described with reference to particular embodiments, it will be understood to those skilled in the art that the invention is capable of a variety of alternative embodiments Within the spirit and scope of the appended claims.

We claim:

1. An apparatus for continuous floating zone refining of an ingot of fusible material containing at least two ingredients, at least one of which has a segregation coeflicient other than unity comprising a container for said ingot, said container having mutually opposed openings through which said ingot extends,

ports in said container for admission of and removal of gaseous material within said container,

means for supporting said ingot within said container,

said means comprising a pair of grips within said container ingot,

means operatively connected with said means for supporting and for stretching said ingot, and

heating means around said ingot and mounted for movement along said ingot for heating a narrow zone thereof.

2. An apparatus as defined in claim 1 wherein said ingot extends through said container, said container having sealing means mounted thereon through which said ingot may have movement.

3. An apparatus as defined in claim 2 including die means within said container proximate to said sealing means.

4. An apparatus as defined in claim 1 wherein said container is comprised of a main body portion, and

a pair of separable elongated end portions in a sealing relationship with said body portion.

5. An apparatus as defined in claim 1 wherein said grips are adjustable from a tight fit to a loose fit with respect to said ingot.

6. An apparatus as defined in claim 1 wherein said grips comprise rollers in tight engagement with said ingot.

7. An apparatus as defined in claim 5 wherein said rollers are serrated.

8. An apparatus as defined in claim 1 wherein said means for stretching said ingot comprises movable magnets.

9. An apparatus for continuous floating zone refining of an ingot of fusible material containing at least two ingredients, at least one of which has a segregation coeflicient other than unity comprising a container for said ingot, said container having mutually opposed openings through which said ingot extends,

ports in said container for admission of and removal of gaseous material within said container,

means for supporting said ingot within said container,

said means comprising a pair of grips within said container for engaging said ingot,

for engaging said means operatively connected with said means for supporting for stretching said ingot, and heating means around said container for melting a narrow zone of said ingot, said heating means being movable along said container. 10. An apparatus as defined in claim 9 including means for measuring the amount of stretch of said ingot.

11. An apparatus as defined in claim 9 wherein said means for supporting said ingot includes spring biased rollers secured to said container.

References Cited UNITED STATES PATENTS 2,964,396 12/1960 Rummel et al l48l.6 3,030,189 4/1962 Schwcickert et al 148-15 L. DEWAYNE RUTLEDGE, Primary Examiner.

I. E. LEGRU, Assistant Examiner.

US. Cl. X.R. 

